Electronic equalization of transmission impairments

We have reviewed experimental and numerical results on electrical signal processing for the reduction of penalty induced in the optical domain. Since a few years integrated electronic equalizer circuits are available for 10 Gb/s operation. Penalty reduction of signal distorted by chromatic dispersion, PMD, and self-phase modulation has experimentally been demonstrated. First studies on equalization of DWDM typical crosstalk have already been conducted. Nevertheless, as compared to the decade long experience with dynamic equalization of thermal noise limited signal, for amplified optical signal limited by the optical signal-to-noise-ratio (OSNR) the residual penalty after equalization roughly doubles and the fast responding LMS adaptation leads to a sub-optimum setting of the equalizer failing the optimum by up to 0.8 dB which can be avoided by the slower steepest-descend scheme which optimising Q-factor related criteria at equalizer output.